CA1192072A - High bulk pulp, filter media utilizing such pulp, related processes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The disclosure relates in part to a novel and highly superior high bulk pulp formed of lignin-containing fibers, and to process conditions for manufacture of the pulp. The process involves selection of a lignin-containing fiber source, having a lignin content of at least about 10%, and thermomechanically pulping the fiber source under temperature/pressure conditions of 300°F - 350°F / 50 psig - 120 psig and a refiner energy utilization of about 8 - 35 HPT/ADT, using a double disc, counter rotating disc refiner. The thermomechanically produced fibers are characterized by a high degree of stiffness, and an extremely smooth surface, free of fine fibril formation and thus substantially non-self-bonding. The new pulp has wide variety of specialty uses which are attractive in terms of both economics and technical performance, because of the exceptionally high bulk and other distinctive characteristics of the fiber.
Novel and highly superior filter media, formed using the new pulp which filter media are particularly useful in the filtration of lube oil, fuel and air. The filter media are formed by a random lay-up of the lignin-containing fibers, typically with selected other pulp fibers having technical characteristics suitable for filter media utilization. Suitable lignin-containing fiber, produced under conditions of the invention, may be substituted with minimum effort for conventional technical fibers utilized in furnishes intended for filter media production. The new filter media are characterized by exceptionally high bulk, void volume and dust capacity - high critical characteristics of filter media, and provide equal or superior product performance at significant reductions in production cost and/or exceptional improvement in filtration performance at equivalent production cost.

Description

The present invention relates in part to a new technic~l grade thermo-mechanical pulp, which is characterized by an extremely high buL~ ch~racteristicand high resistance to degradation under paper-making conditions, while at the same time being extremely economical to produce and utilize. Because of these significant characteristics, the new pulp finds adventageous uses in a variety OI
specialty products. Additionally the invention pertains to novel filter media and to the use of such media for filtration, in particular for the filtration of air, fuel, or lube oil.
Thermomechanically produced pulp is a well known product in a general sense. It has been widely used for many years in the production of fiber board productsJ construction paper, newsprint, and other products. For example, in Asplund, U.S. Patent 2,008,8g2, it is disclosed that thermomechanically producedpulp is useful for the production of wall board, insulation board and similnr products, as well as cardboard. (See also Asplund U.S. Patent No. 2,047,170.) U~S. Patent No. 4,219,024, issued to Patience et al, discloses the use of thermomechanically produced pulp, as well as mechanically and semi-chemically produced pulp, in an absorbent article to capture body fluids, comprising a p~d made of a mass of said fibers and particles of p~astic material fused to the fibers in the pad to increase the integrity thereof.
In a thermomechanical pulping process, wood chips or other lignin-eontaining materials are generally placed under a steam atmosphere at elevated pressure. After preheating in the pressurized steam atmosphere, the wood chips are progressively intrcduced between a pair of rot~ting refiner discs while maintained under steam pressure. Depending upon the pressure of the steamS
and the adjustment of the refiner discs, the wood chips are subjected to a controlled degree of abrasion to thereby reduce the chips to fibrous form. The fibers then issue from the peripheral region of the rotating disc refiner for further processing and utilization.

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It has been known that under certain pressure/temperature conditions in a disc réfiner, and certain energy level utili~ation during the refining process, there is a heat softening or thermoplasticity of the lignin within the fiber bundles.
This brings about a weakening of the so called middle lamella, such that the bonding force between adjacent fibers is greatly reduced and the individual fibers are easily separated without excessive damage and breakage. These original discoveries date back to the early 1930s and are reflected in, for example, U.S.Patent No. 2,008,892 and U.S. Patent No. 2,145,851, both issued to Asplund.
Developments in equipment and techniques for the thermomechanical manufacture of pulp have of course cont;nued since the pioneering effort~s of Aslpund. Examples of more recent efforts are the Shouvlin et al. U.~. Patent No. 3,773,610, assigned to Bauer Bros. Co., Springfield~ Ohio, and the Selander et al. U.S. Patent No.
4,22 l,630.
Notwithstanding the more or less continuous development effort over the last 50 years or so in the art of thermomechanical pulp production and the utilization thereof, however, no one has heretofore discovered or recognized thetruly exceptional high bulk characteristics of certain types of thermomechanically produced pulp fibers for use in the manufacture of fibrous filter media and the beneficial use of such filter media in processes of filtration.
It has now been discovered, however, that thermomechanically produced pulp fibers, produced under certain controlled conditions as specitied herein, result in a pulp and fiber which is nearly a theoretical ideal for use in the mamlfacture of fibrous filter media and for other end uses wherein the high bulk and other desireable characteristics of the pulp are important. Such thermomecharlically produced pulp fibers are far superior to ordinary chemical pulps utilized for these purposes, and indeed superior in many respects to the so-called high performancechemical pulps.
The new pulp is derived by the thermomechanieal production in a disc refiner of pulp from lignin-containing source materials having a lignin content of at least about 10%. Under the conditions of the invention, the lignin-containingsource material is processed under considerable steam pressure, in a range of about 50 psig to about 120 psig, at temperatures in the range of about 300F

to about 350F. Additionally9 the disc refiner adjustments are such that, under the specified pressure/temperature conditions, there is an energy utilization inthe fiber production of about 8 to about 35 Horse Power Days pe~ Air Dried Ton (HPD/ADT) of the material. These conditions, as will be explained more fully hereinafter, enable the production of a technical grade pulp material which has a uniquely advantageous fiber structure for a variety of paper and board products in which low apparent density ;s one of the desirable attributes. In particular,the pulp has extraordinary advantages when incorporated in filter meclia.
Felted nonwoven matsrials are widely used in the manufacture of filter media, for example, such as automative oil, air and fuel filters. Such filters are presently manufactured in large volume by conventional, wet paper-making processes, although air-laying is also a viable and potentially pref erable manufacturing procedure. Ideal material.s for -filter media are bulky, porous, strong, stiff, resistant to heat and chemical degradation, and insensitive to water.
The media also should have a desired average pore size for its intended function.
These various desirable attributes can generally be controlled by varying the fiber furnish, the treatment of the fibers prior to forming, the manner in which the web is formed, and the post treatment of the formed web. The post treatment, for example, may include any or all of the following: pressing, drying, binder

2 0 addition, and corrugation.
Physical ~haracteristics of the fiber are of course highly significant.
In this respect, experience indicates that ideal fibers should be relatively strong and stiff. They should also possess some degree of curl, yet be relatively non-bonding. Currently, chemical pulps are widely utilized in the production of fibrous filter media because the chemieal pulps are characterized by a greater fiber length, higher individual fiber strength and stiffness, and a relatively large degree of fiber bonding when made into paper. By contrast, conventional ground wood pulps are very short, leading to a filter sheet which lacks desired strength and porosity, among other things.
Vnfortunately, the most desirable grades of chemical pulps for use in the production of fibrous filter media are also extremely expensive. One such

3-commercially available chemical pulp, i.e~3 a mercerized southern pine, forms the basis for a super;or type of conventional filter sheet possessing a low level of fiber bonding, along with high porosity and high bulk. However, the chemical process for the manufacture of this pulp is rather comlex9 and the yield of pulp is quite low, i.e., about 3596 based on oven dry wood. Accordingly, this pulp is very costly. Some of the other chemical pulps, particularly flash dried kraft, are somewhat less costly but are correspondingly less satisfactory on a performance basis, and their use is limited to applications in whieh the performance specifications of the filter media are less demanding.
In accordance with one aspect of the present invention, a novel and greatly irnproved filter media is provided, as well as efficient processes of filtration utilizing same. The filter media of the present invention utilizes thermomechanically formed pulp in lieu of some or all of the content of high performance and other chemical pulps otherwise customarily utilized.
Nevertheless, not only is there no significant loss in filter performance characteristics, but there is indeed an improvement in some of the more significant filter characteristics as a result of the substitution. Additionally, where the new filter media incorporates thermomechanically formed fibers in lieu of lower performance fibers, such as flash dried krafts, a significant performance benefit 20 is realized in the use of the filter media in filtl-ation processes.
The filters of the present invention are characterized by an exceptionally high dust capacity, high freeness, high void fraction and high bulk, all highly desirable characteristic~ of filter media. In many respects~ the filters Oe the present invention exceed the performance charaeteristics of conventional filters using high performance chemical pulps. Moreover, the filters of the present invention are capable of achievin~ superior performance in a broad spectrum of filtration processes, and in particular, in processes for filtering air, lube oil, fuel or pharmaceuticals.
One of the fundamental aspects of the present invention is the 30 production of a new technical grade of mechanical pulp under selected and controlled thermomechanical conditions. The pulp fibers derived from this pulping~

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process have uniquely desirable characteristics for incorporation in filter rnedia, for example, and in selected other end products in which a high bulk, low density structure is desirable. For convenience of reference, the pulp fibers so produced may be frequently referred to herein as lignin-containing fibers, as one of the characteristics thereof is that most of the original lignin content is retained in the final fiber.
It is believed that the source of the li~nin-containing fiber is not specifically critical and may be taken from a wide variety of lignin-containing fibers, although some may, of course, be preferable to others. These sources include debarked wood (both softwood and hardwood varieties) and other lignin-containing materials, such as bamboo, bagasse, eertain grasses and straws, and the like. For purposes of the invention, the fiber-forming material should have a lignin content of at least about 10% and preferably around 15% or moee (most pulp woods have a lignin content in excess of 20%). At the present state of development, the preferred fiber source is debarked wood, either northern or southern softwoods or hardwoods, with some preference toward northern softwoods.Eucalyptus is also a preferred source of lignin-containing fiber.
In the case of debarked wood, after removal of bark, which is not used in the process, pulp wood logs are cut into chips, or some other reduced form, of a size suitable for thermomechanical processing. Desirably, the typicalchip size is in the range of 3/8 inch by 1/2 inch by 3/4 inch, with the fibers aligned with the long axis of the chip. Of course, in any chipping process, the size and shape of the chips is highly randomized. Nevertheless, the objective isto seek a typical chip having a minimum dimension of about 3/8 of an inch nnd a maximum dimension of about 3/4 of an inch7 whieh can be reasonably approximated by screening of the chips through one inch maximum screen mesh and 1/8 minimum screen mesh.
The screened chips, typically after cleaning by a conventional water wash procedure, are reduced $o pulp fibers following the general techniques of the Asplund U.S. Patent No. 2,008,892, or the Shouvlin et al U.S. Patent No.
3,773,610, the disclosures of which are expressly incorporated herein by reference.
A first step in the process is generally the preheating of the chips by steam, and this is advantageously carried out in a vessel such as a horizontal tube digester. The digester, which is a conventional piece of equipment, may be provided at the inlet with a rotary valve or similar device (also convention~l) for aceommodating the in-feed of wood chips while maintaining the vessel under superatmospheric steam pressure.
In the process of the invention, lignin-containing material in reduced form OI suitable size, e.g., as in the aforementioned sizes for wood chips, is preheated at a temperature not less than about 300F and more desirably at a temperature in the range of about 330F to about 350F. This corresponds to a pressure range of about 50 psig to about 120 psig, with the preferred range being from about 90 psig to about 120 psig. Desirably, the wood chips are moved progressively through a partially filled (1/3 to 1/2) digester, while being continually agitated. This assures highly efficient heat transfer between the steam and the wood chips and a uniform preheating. Typically, a three minute retention time inside the horizontal tube digester is adequate, and this is believed to bring the inside of the chip to within about 10F of the steam temperature.
The preheated wood chips are then ground into pulp fibers in a disc refiner, while the chips are maintained in a pressurized steam atrnosphere and in their substantially dry condition. Grinding is performed in a disc refiner of 20 the general class disclosed in the before mentioned Asplund or Shouvlin patents.
More specifically, however, a C.E. Bauer, No. 418 counter rotating 36 inch double disc refiner is a preferred piece of equipment for this purpose. This machine utilizes a pair of oppositely rotating 36 inch discs arranged in communication with the horizontal tube digester and arranged to receive preheated wood chips from the digester, (preferably under the same pressure conditions), in which case a pressure valve device is not required to be located between the digester and the disc refiner.
In accordance with generally known principles, when the wood chips are subjected to shear and abraded by the counter-rotating refiner discs, they 3 o are subject to further heating as a result of the energy input of the grinder itself. It is known that under certain conditions of preheating of the chips and operation of the disc refiner that the lignin content of the chips becomes softened and plasticizsd, thereby allowing easy separation of the individual fibers with minimum damage and destruction of the fibers. A desired degree of refining is controlled by fldjustment of the peripheral gap between the refiner discs. In general, the narrower the gap, the more energy utilization that is required to refine the pulp and enable the fibers to emerge from the gap. Typically, such energy utilizaion is measured in Brake Horse Power Days per Air Dried Ton (HPD/ADT) of the raw material. For the production of pulp fibers according to the invention, ideally suited for the manufacture of filter media and other high bulk end produets, it has been determined that the energ~ utilization in the disc 10 refiner should be not less than about 8 HPD/ADT and not more than about 35 HPD/ADT. In many cases, achieving the desired energy levels requires setting oE the gap at minimum size - v;rtually zero clearance, although forcertain woods, such as southern softwoods, it may be desirable to widen the gap slightly in order to limit the energy to around 35 HPD.
After refining, the fibrous pulp is discharged from the refiner through a suitable blow valve or the like, which enables the fibrous material to be taken from a pressurized condition to a nonpressurized condition.
After the disc refining operation, the pulp fibers are generally mixed with sufficient water to derive a slurry of about 0.5 to 1% solids, suitable for 20 screening of the fibers. In this respect, fibers produced according to the procedures outlined are significantly longer and stiffer than more conventional pulp fibers and are not readily screened on conventional pulp sereens without excessive rejection of good fibers and ~mnecessary loss of yield. Because of the fiber characteristics of the pulp thus produced, it has been found to be desirable to utilize a rotary-type screen having slots aligned circymferentially (rather than axially as is more typical). A s~called "Ultrascreen't marketed by Black-Clawson is effective in the present process. Such a screen having a slot width of approximately six mils enables effective screening of the pulp with reliable rejection of shives and other foreign matter, yet without excessive rejection of 30 good fiber.
Various pulp wood samples, processed under a variety of pressure-temperature conditions and refiner energy leveLs gave fiber characteristics as set forth in the following Tables I and II. These characteristics are compared with several com m ercial pulps in Table 11.

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Rlectron photomicrographic studies were rnade of selected samples of the ~ulp woods processed as set forth in Table I. These were compared against conventional, commercial pulps Icnown to be advantageous for utilization in the production of filter media. The latter included flash dried Westvaco pine, flash A dried Westvaco hardwood, Buckeye "HP~ Buekeye 512 cotton linters, JR-Berlin Bleached kraft softwood and hardwood (not flash dried). The Westvaco products are sold by Westvaco under t~e c~ommercial characterization "Pinnacle Prime"
softwood and "Pinnacle Prime"Yhardwood. "HPZ" is a commercial characterization for a high quality mercerized southern pine alpha pulp by Buckeye Cellulose.
In the examination of fibers produced under the pulping conditions of Table I, a spectacular difference in fiber surface was observed in both hardwood and softwood pulps as the steam pressure used in preheating was increased. At low steam pressures (15 psig) the process yielded a fiber having a large amount of fine structure. Parts of the cell walls were peeled from the fiber surface, fibers were rough surfaced, and fibrils could be observed that bonded one f;her to another~ As steam pressure was increased to about 50 psig, a change in the surface structure development was observable, i.e., there was less fine structure which bonded the fiber together. The pulps made at 90 psig steam pressure were absolutely smooth walled. Even at 800~ magnification there was no fibrils, no hint of sureace development and the fiber surface appeared undamaged. Pulps made at 120 psig steam pressure were free of the fine surface structure development that was apparent at 15 psig, but there was an indication that softwood fibers may have been damaged (although filter sheets produced therefrom appeared to have excellent filter qualities). Some o-f the softwood fibers at 120 psig were actually split open to reveal the lumen. The walls, neYertheless, possessed a smooth, non~bonding appearance, as was observed in fibers produced at 90 psig steam pressure. Hardwood pulps produced at 120 psig did not have the appearance of possible damage as did the softwood pulp. Indeed, they looked more or less the same as those fibers produced at 90 psig.
In the case OI JR-Berlin hardwood and softwood pulps, as well as Allied softwood pulp, the fibers had a ribbon-like appearance and tended to collapse when dried so that one fiber bonded to another. By way of comparison, under high magnieicat;on, the fibers produced in accordance with the present invention tended to look lilce "uncooked spaghetti" while the more conventional kraft fibers had an flppearance of "cooked spaghetti". Even though the conventional kraft pulps had not been refined, there was evidence of surface fine structure fibrils which bonded one fiber to another.
The Westvaco hardwood and softwood pulps, under h;gh magnification, had the appearance of 'tkinky ribbons". The Westvaco fibers collapsed, like the JR-Berlin and Allied fibers, but there aplpearecl to be little bonding between f;bers. Fibers made under the conditions of the invention looked like rigid, 10 straight rods as compared to the Westvaco fibers. The latter had a radius of curvature of the "kinky" portion which appeared to be on the same order of magnitude as the fiber diameter itself, which was an unusual charaeteristie.
The 13uckeye "HPZ" fibers, which are generally regarded as the highest quality of commercially available pulp for filter media purposes, appeared to be in the form of curly rods. The radius of curvEIture of the curls was much greater than that of the "kinks" present in the Westvaco fiber. The "HPZ" fiber had an observable fine structure which was noted, however, to be relatively rigid and non-bonding.
Photomicrographs of the Buckeye 512 cotton linter pulp showed the presence of 20 "curly rods" with a surprisingly large amount of -fibrils present, which tended to bond the eibers together. The fibers themselves were not flexible enough to bond, as in the case of the kraft pulps, but the fine structure was flexible enough to contact and bond adjacent fibers.
In general7 fibers produced under the conditions of the invention were more rigid and less conformable than the kraft fibers. Those made under the higher steam pressure conditions were very smooth surfaced. In physical appearance, fibers produced under the conditions of the invention looked more like the Buckeye "HPZ" than any of the other pulp fibers studied. Accordingly, as will appear hereafter, in filter media products in which fibers produced under 30 the conditions of the invention were substituted for "HPZ" fibers, corresponding or better filter performance was achieved in a filtration processO This is remarkable, indeed, considering that fiber yield for pulp produced under the conditions of the present invention is significantly higher than the yield in the prod~ction of high performarlce chemical pulps such as "HP~".
In the produetion Oe pulp for end use in filter media, perhaps the most significant specification is freeiless, which is a conventional measure of the openess of the structure of the pulp fibers. In this respect, pulp produced in accordance with the conditions required by the process ~ the present invetion has exceptional freeness, approximating 760+15 ml ~ t. This compares most A favorably with the typical freeness value of about 750 for Buckeye "HPZ", a superior grade but costly, commercially available filter pulp.
In the manufacture of conventional filter media, frequently produced 10 in the form of a continuous web of material, it is typical and usually desirable to combine two or more pulps in order to obtain a combination of desirable characteristics in the end product. This is also true of improved filters made utilizing lignin-eontaining pulp fibers made in accordance with the speeified conditions of the invention. In this respect, one of the characteristics of a good filter fiber is its relatively non-bonding character, which tends to result in low tensile strength in the end product. Accordingly, it is advantageous to combine the lignin-containing pulp fibers of the invention with more conventional, relatively low cost flash dried kraft pulps for additional tensile strength. The finished web is~ in any event, typically impregnated to some degree with a binder resin (typically 20 phenol-formaldehyde) which produces effective fiber bonding without filling the interstiees of the media itself.
Although it is contemplated that filter media using the lignin-containing fibers of the invention may be produced using, for example, air-laying techniques, most filter webs currently are produced by more conventional web paper-making processes. To use this endS it is common for the several pulps to be combined together in a beater to acheive a uniform mixture before the fiber slurry is laid on a paper-making screen. The new pulp fiber produced under conditions of the invention is highly advantageous in this regard, as the fibers, in addition to having a high degree of stiffness, and strong and tough, and little affected by water, 30 whereas the commercially available ~ibers, whieh initially may be somewhat equivalent in desirable properties, are highly brlttle and subjeet to severe degradation in the beating process. Although as a praetical matter a relatively %~

few minutes of beating time may be adequate, typical mill practice usually results in a greater-than-necessary amount Oe beating time with resultant product degradation. Th;s is a particularly serious matter in connection with the use of a pulping product such as "HPZ1', which is seriously degraded in its per~ormance characteristics by the usual beating operations.
Likewise, after initial forming Oe the filter web, it is desirable occasionally for the web to be pressed before impregnation. This can also degrade high performance chemical pulps and can cause undesirable densification OI webs produced with less costly kraft pulps. On the other hand, such pressing has relatively little effect on the lignin-containing fibers produced under conditions of the invention or on the density of pulps produced under the conditions required by the invention.
Thus, among the important advantages of the use of selected lignin-containing fibers produced under the conditins of the invention in a filter web material is its ability to withstand the preliminary beating and pressing operations without significant degradation and without significant densification. More conventional high performance pulp fibers are susceptible to one or both of these shortcomings.
~ ilter media incorporating significant percentages o~ lignin-containing pulp fibers produced according to the conditions of the invention exhibit marke~ly superior "dust capacity" than corresponding filter media using conventional pulps, including even the high performance chemical pulp. This is a function of the very high freeness of the pulp and the correspondirlgly low apparent density.
As reElected in Tables I and Il, pulp freeness is markedly affected by p~ steam pressure condit~ns during preheating and refining. Below 50 psig, freeness characteristics ~ ) are well below ~00 and shive content is relatively high, whereas pulp produeed amder conditions of 90 and 12û psig had freeness characteristics of greater than 750 and as high as 770 and minumum shive content.
Pulp possessing these outstanding freeness values, combined with the stifIness, 3n toughness and non-bonding charcteristics, c~n result in a superior filter media having a very high bulk and correspondingly high dust capacity.
By way oi example, test sheets were prepared with several 7~

commerciaUy signific~nt pulps usecl in the production of filter media, including (~

JR-Berlin softwood kraft, Buckeye "HPZ" and -~lpha ~ulp, such as "Placetate"
marketed by ITT-Rayonier. All sheets were beaten for five minutes to stimulate mill condition~s, but were ~mpressed. Table III below indicates values for basis weight in pounds per 3000 sq. ft.; web caliper in mils; dust capacity in grams per kilogram; tensile strength in pounds per ineh; and void fractions.
TABLE III
Sin~le-Pulp Sheets, Unpressed~Beat Five Minutes (Sheet of Buckeye Alpha J R-Berlin Invention) "HPZ" Pulp _ Softwood Kraft Basis Weight i~5 65 6~
Caliper (mils) 0.040 0.019 0.û20 0.016 Dust Capacity (g/kg) 3367 732 952 29.3 Tensile Strength 1 1 2 16 Void Fraction 0089 0.83 0.85 0.75 As will be readily evident, the dust capacity of a filter sheet made in accordance with the teachings of the present invention is markedly superior tothe dust capacity of sheets made from any of the other fibers. This particularly significant since dust capacity is directly related to the useul life of a filter.
For example, it is contemplated that an automobile engine oil filter using filter media produced in accordance with the invention may realistically have a useful life of 509000 miles.
Another notable feature of filter media manufactured in accordance with the invention and evident from Table III is the extremely large caliper or bulk of the filter sheet of the invention. It is approximately twice the caliper of sheets made with high perEormanee chemical fibers. Among the many ramifications of the combined extraordinarily high values of caliper and dust capacity of the new filter media are its ability to provide a much thieker and therefore desirably stif~er filter web at a given basis weight, such web having, of course, outstandingly superior dust capacity to conventional filter sheets.
30 Alternatively, it is feasible to recluce the weight of fiber in a sheet of given ~aliper, producing a sheet which still possesses a dust cap~city superior to conventional filter sheets.

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The example sheets of Table III were prepared using a single pulp fiber. More typically, however, in commercial pratice a filter sheet will be comprised of a plurality of fibers with each contributing certain desired characteristics so that the filter media may be optimized for a given end use function TABLE IV
COMPARISIONS OF STANDARD AND NE FILTRATION MEDIA

Standard Furnish Furnish with LCF
Fiber PuLp/% HP~/38.3 LCF/75 Pulp/% W/VP/46.4 W/VP10 Pulp/% Polyester/15.3 Polyester/15 Cured Basis Weight 126 128 Caliper, inch 0.044 0.û56 Permeability, Frazier 72.4 76.2 MD Stiffness~ mg 5950 6800 CD Sti~fness, mg 2500 2600 MD Tensile, lb/inch 22 18 CD Tensile, lb/inch 9.5 7.2 Mullen, psi 29 16 Groove Depth~ inch 0.015 0.016 Resin, % 16 16 Volatile, % 5.6 6.0 MFP, mm 0.021 0.028 ~Lignin Containing Fiber (LCF) produced according to the cond;tions of the invention.
TABLE V
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~TANDARD AND NEW FILTRATION MEDIA
. _ __ __ Standard New (LCF) Basis Weight lb/300û ft.2 126 128 Pl~at Width, inch 4.022 4~21B
Pleat Height, inch 0.75 0.75 -16~

Pleats ;n Filter S9 48 Area in Filter, inches square 356 304 Caliper, inch 0.044 0.056 Groove Depth, inch 0.012 0.015 Filter Life, Hours 15.7 20.9 Dust Capacity of Filter, g 34.8 45.9 Dust Capacity, /mg Filter Media, g 73~ 112 Dust Capacity, /sq. inch Filter Media, g 0.0976 0.151 Weighted Average Efficiency 88.3 88.3 In Tables IV and V, there are set forth two different sheets of filter media, a control sheet utili2ing high performance chemical fiber (Buckeye IlHpZtl) and a second sheet utilizing a similar (but not identical) combinatin of fibers in which the high performance chemical fiber was replaced entirely by lignin-containing fibers produced in accordance with the conditions of the invention (identified in Table IV and V as "LCF"~, with changes in the proportions of the other fibers. In Table ïv, the characteristics of the filter sheets were measured after the s~turation of the sheet with phenolic resin and euring. In the sheet indicated in rables IV and V, the pulp furnish for the control sheet included approximatel~ 38.396 "HPZ", approximately 46.4% Westvaco so~wo~d (Pinn~cle

4~ Prime Pine), and approximately 15% polyester (DuPont Dacron~ 0.~5 inch long and 1.5 to 3.0 denier). In the comparison sheet, made with "LCF" fiber, the polyester fiber content was unchangedl the Westvaco softwood fiber content was reduced to 10%, and the remaining 75% OI the furnish was made up of "LCF"
lignin-containing fiber produced in accordance with the conditions specified by the invention.
The data presented in Table V demonstrate the superior ealiper of paper made from "LCF" fiber. The control paper was found to be 0.044 inch thick while the paper made from the "LCF" fiber was found to be û.056 ineh thick. Since the two papers have the same basis weight, the void fraction of the paper made from the "LCF" fiber obviously was much greater than the void fraction ne the control paper. Void fraction can be calculated from the equation:
V = 1 - (U.0000as58 Basis Weight/Caliper).

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Using the equation, one finds that the void fraction of the control paper is 0.869 while the void fraction of the paper made by using the "LCF"
Eiber is 0.895. This difference in void fraction is related to the higher dust capacity of the paper made from an "LCF" containirlg furnish.
The performance of the two sheets of filter media is summarized in Table V. For this comparison, lube oil filter elements were made by pleating strips oE the two papers. The element containing the control paper was made with the standard number of pleats, which is 5~. The element made with the second paper, which contained the "LCF" fiber~ contained only 48 pleats. Thus, the standard element containing the control paper had a filter surface area OI
356 square inches while the element made with lignin-containing fiber has a surface area of only 304 square inches, an area reduction of about 15%.
In spite of the reduced filter surface area, the element containing the "LC~" fiber possessed a useful life of 20.9 hours while the element containing the control paper possessed a useful life of only 15.7 hours. This difference in dirt holding capacity between the control paper and the paper containing the "LCF" fiber is more impressive when one examines the dirt holding capacity on the basis of grams of dust per kilogram of filter media. When examined in this way, the element containing the paper made with "LCF" possesses a dirt hol~ing 20 ratio of 1126 g dirt/kg paper while the element containing the control paper possesses a dirt holding ratio of 738 g/kg. Thus, on the basis of equal weights of ilter media, the element made with "LCF" fiber would hold 1S2% of the dirt held by a standard element made with the control fiber furnish. This fact is even more impressive when one learns that the paper chosen as the control for the example is a premium quality sheet which is used only in the highest perforrnance lube oil filters.
The unique high caliper of paper made from a furnish containing "LCF"
is of value in filtration products for the superior dirt holding capacity, as has been shown. The unique high ealiper also benefits product runability on pleating 30 lines and results in a desirable high stiffness in the finished product. Many filter products m&de from nonwoven webs such as paper are pleated prior to placement in a filter element, because pleating allows one to increase the filter area that ~2~
;s exposecl to the fluid flow. Accordingly, one of the important characteristics of successful filter l-nedia is their ability to pleQt. Experience has taught that the paper must possess a certain minimum caliper and stiffness if it is to run through commercial pleating equipment successfully. To a large extent, many filter products are made at the lowest basis weight that will pleat successfully.
Papers made with a furnish containing the new "LCF" fiber are both thicker and stiffer than paper made from a furnish containing commercially available fiber.
Thus, it is observed that paper made with a furnish containing "LCF" is superior in its pleatability because of the increased caliper and increased stiEfness. It has also been observed that one can make a lower basis weight furnish which contains conventional commercially available fibers. Thus by using "LCF" fiber in a paper with a lower than standard basis weight one can produce a filter paper which pleats well, possesses equivalent or superior dust capacity, and possesses equal or superior paper stiffness.
Product stiffness is a very important characteristic of successful filter media. In a filter element which is filled with pleated filter paper~ the ability of the media to wi thstand collapse due to hydrdaulic loading is related to the paper sti-ffness. The stiffness of a strip of paper is proportional to the thickness to the third powerO Since the paper made from a furnish containing "LCF" fiber is thicker than paper made from conventional commercially available flbers, the stiffness is significantly improved.
Filter elements are usually evaluated on the basis of their dust capacity and their dust removal efficiency. The dust capacity of filters made of media containing ~'LCF" fiber has been shown to be significantly higher than the dust capacity of filters made of media containin~ conventional pulps. Filters made of media containing LCF fiber in accordance with the new present invention generally exhibit a dust capacity of at least 1460 g/kilograrns. Indeed, filter media having a dust capacity of at least 2190, and even 2930g/3cg or more, can also be readily attained in accordance with the present invention. Such outstanding dust capacity demonstrates the unique applicability of the media of the present inventicn to filtration processes.

Generally, the filter efficiency of high dust capacity media is usually found to be lower than the filter efficiency of media with a lower dust capacity.
This is not true, however5 with filter elements made with the new "LCF" fiber.
It is thought that the extra thickness, which is obtained with the "LCF" containin~
furnish, increases the len~th of the flow path. This provides a longer period of time for the particles to be within the web structure which, in turn, increases the probability of par1icle-to-fiber impaction and retention. Thus, it is found that the elements made vvith an "LC~" fiber containing media possess a partlcle removal efficiency that is equal to the efficiency of elements made with conventional fibers. Aecordingly, filtration processes, for example, involving the 10 filtration of air, lube oil, fuel or pharmaceuticals, by passing same through filtration media, are most efficient when the filter media of the present invention is employed.
In the manufacture of filters for commercial use, it is typical practice to comb;ne a specific pulp mixture calculated to achieve desirable properties for a given end use. Iypically, although not necessarily, the pulp mixture is prepared as a slurry, beaten sufficiently to assure uniform distribution, and then wet laid on a paper-making screen. Also typically, the wet web is dried and then impregllated with a binder resin. The resin, typically, is only partially cured by the web manufacturer. The ultimate filter mamlfacturer, usually converts the 20 web material into a accordion pleat configuration, quite frequently forming a cylinder of accordion pleats accommodating a generally radial flow of the eluid media to be 3iltered. At this stage of production, the resin in the web material may be fully cured to provide a relatively permanent set to the manufacturer's configuration. Such a eilter media structure comprising a cylinder of accordion pleats, and with media being innpregnated with binder resin, is quite common in automotive filters~ e.g. oil filters, fuel filters or air filters.
In a typical filter web intended for use as an auto air filter, for example, conventional pulp furnish may consist of approximately 60% high performance ehemical pulp, such as "HPZ", and about 40% flash dried pine, such 30 as Westvaco "Pinnacle Prime" softwood. It is contemplated that in such a filter furnish, a large portion, preferably all, of the "HPZ;" component can be replaced by the lignin-containing fibers produced under conditions dictated by the invention.

The resulting web product is of equal or superior performance. Indeed, the ama~ingly superior dust capacity of the new filter material is such that the overall ~ilter life rmay be extended dramatically over existing products.
In a filter intended for use as a heavy-duty air filter in off-road vehicles, for example, a typical conventional furnish might comprise approximately 50% flash dried southern pine and approximately 50% flash dried hardwood, such as Westvaco "Pinnacle Prime" hardwood. It is contemplated that in such a furnish both of the flash dried components may be entirely or partially replaced by li~nin-containing fibers derived under the conditions of the invention, thereby resulting in a filter product having significantly superior performance characteristics.
Several fiber furnishes are typically employed in the production of filter web for automotive oil filters. For long life, heavy-duty service, the typical furnish may be approximately 60% high performance chemical pulp, such as '~HPZ", approximately 2596 l~ash dried southern pine and approximately 15% polyester (DuPont Dacron, as previously described). A somewhat lower quality furnish consists of approximately 45,6 Alpha pulp, such as the before identified product of ITT Rayonier, approximately 50% flash dried southern pine, and approximately

5% polyester. A somewha$ lower quali$y furnish consists of approximately 50%
flash dried southern pine, approximately 45% flash dried hardwood and approximately 5% polyester. In the higher quality furnishes, the high performance chemical pulps ("HP~", Alpha pulp) may be replaeed substantially or entirely by the lignirl containing fiber pulp produced under conditions of the invention. In the lower quality furnish, the ~lash dried southern pine may be replaced substantially or entirely by the lignin-containing ~ibers. In the case of the higher quality furnishes, the substitution results in equal or even superior performance, whereas in the lower quality furnish7 the substitution results in a dramatic increase in performance.
A typical automotive fuel filter furnish comprises approximately 60%
flash dried southern pine and approximately 40% Elash dried hardwood. In that furrlish, the new lignin-containing fiber may be substituted for all or a sbstantial part of the flash dried southern pine with significant increase in Eilter performflnce.

Filters intended for pharmaceutical u~;e typically rnay contQin approximately 60Yo high performance chemical pulp, such as "HPZ" and approximately 40~O ~otton linters. The new lignin-containing fiber may be substiluted for some or all of these components in such filter furnishes, with equal or better performance at dramatic cost savings.
In hydraulic and/or high efficiency fuel filters, a typical furnish may consist of approximately 30% alpha pulp and approximately 70~/O flash dried hardwood. The new fiber may be substituted for all or part of the alpha pulp component of sueh furnishes, with equal or better performance.

LO The above examples are intended to be illustrative, and not be any means limiting. It is anticipated that because of the coincidence of outstanding performance characteristics and favorable production cost which is achieved in filters using the lignin-containing fiber produced under conditions of the invention, that filter media will be designed and constructed to maximize use of the new fiber, and it is contemplated that filter furnishes and filter media may be eonstituted exclusively of the new fiber in some instances.
One of the important economic advantages reali~ed by the invention is derived rom the extremely high yield of fiber from the ~splund-type pulping procedure. Thus, fiber yeild may be as high as 95~6 of the dry wood starting material as compared to chemieal processes for high performance pulp, which yield as little as 35% useable fiber. To a large extent, this results from the fact that the fiber output of the pulping process retains substantially all of the lignin and hemieellulose content o~ the original unpulped fiber source. The chemical processes, on the other hand, substantially remove lignin and hemicellulose, whieh results in an immediate loss of yield. Moreover, beeause of the essentially Eragile nature of the resulting fiber product, additional significant losses occllr throughout subsequent processing. The presence of the lignin and lignin related materials in the fiber output is significantly advantageous in the ultimate filter media when the fiber production has been achieved under the conditions of the inventionO Thus, under proper pressure and temperature eonditions, the lignin materials are in a plasticized state during the reIining operation, which not only enables a relatively long, relatively undamaged fiber to be produced, but the resulting fiber is extremely stife and tough, r elatively straight and has a very smooth outer surface free of fibril ~ormation. Tnis structure is ideal for filter media utilization as it exhibits exceptionally low bonding characteristics and, because of its structure resembling "uncooked spaghetti", results in an extremely porous, bulky media when laid in random form, for example, as by wet laying or air laying. Oirectly related to the high bulk characteristie, is an extremely high freeness, in the area of 7G0 and above. This equals or exceeds the freeness of the highest quality high performance chemical pulps.
Filter media prepared in accordance with the invention, being characterized by extremely high blllk and extremely high freeness, have correspondingly exceptional dust capacity, which is a standard measure of useful working life of a filter media. A filter media manufacture, utilizing a portion of the new lignin-containing fiber in Q filter furnish, has a great deal of production flexibility. Because of the exceptional bulk of the pulp fiber, it is possible to produce filter media of equivalent physical characteristics, with equal or superior performance, using web material of significantly lower basis weight than before.
Alternatively, significant improvement in performance can be realized utilizing web materials of simil~r basis weight. As will be evidentl this flexibility enables the manufacturer to exert a wide degree of control over production cost/performance characteristics relationships.
Although the lignin-containing fiber produced according to conditions of the invention has a relatively low fiber bond strength characteristic, the loss of strength is exceeded by the increase in dust capacity such that at any given level of dust capacity a filter media aceording to the invention wil1 have greater strength than a ~onventional filter media.
One other significant characteristic of the lignin-containing pulp fiber derived from the invention is its substantial stiE~ness. This minimizes fiber deformations during lay-up and any subsequent pressing or other operations, assuring that the final media has and retains a very high bullc characteristic.
Moreover, the character of the fiber after discharge from the disc refiner and subsequent screening is such that secondary refining is not necessary. But where 97~

it is desirable to r efine a furnish which is n blend of dif ferent fibers, the lignin-containing fiber will be found to be less damaged than commercially available high performance chemical fiber.
Perhaps because OI their high retained lignin content, the pulp fibers produced under the conditions of the invention remain highly active, chemically.
This facilitates bleaching or other chemical modification of the pulp, which may be desirable for certain applications, such as automotive air filters, for example, where the darkening of a white filter web media with use gives an indication of need for replacement.
Filter media constructed according to the invention also is characterize by an extremely high void fraction, resulting in a media which has an extremely high permeability. Filters made of a web media containing LCF fiber in aecordance with the present invention generally exhibit a void fraction of at least 0.80~ with void fractions of at least û~85 and most preferably even at 0.89 or more also being readily attainable. Such a high void fraction is of course desirable in a filter media as permeability is a measure of the ease with which a gas or liquid is capable of passing through the media. Void fraction also irnparts to the media an unusually high ability to absorb and hold large volumes of fluid.
While one of the most advantageous uses for the new pulp is in the 2 0 production of filter media9 the unique fiber structure and other characteristics ol the pulp make it useful to advantage in other products, for example, products in which low apparent density is a desirable characteristic. Examples of such are non-metaUic liner, blotting material, saturating gasket, endcap and edge filter, battery board and matrix board. In addition, there are many other specialty paper products which may utilize to advantage the high bulk and other physical and chemical characteristics of the pulp. Examples of these further products are: towelling, release bases, baking pan liner, coaster materials, mat board, file folder, press pad, vacuum bag, saturating krafts, battery separator material, shoeboard, album, cap board, die wipe, speaker cone, contruction paper, and mounting board. The new pulp fiber also eontains a high degree of chemical reactivity, which can be taken advantage of in certain later processing operations.

The stiffness and toughness of the smooth, lignin coated fiber of the new pulp material gives important ndvantages in the various processin~ operations that may be required. For example, if the pulp is to be dewatered and bailed for market pulp, the pulp fibers suffer mimimurm degredation while being pressed to remove water and in the subsequent fiber hnndling. Likewise, where the fiber is used in the forrnation of wet material by wet-laying processes, both the fiber structure and the uniquely high bulk characteristic of the wet material are little affected by wet pressing operations. The lignin coated fibers of the new pulp material can also be heat pressed, at a temperature sufficiently high to cause some flow and rearrangement of hemicelluloses and lignin, and enabling the fibers to be bonded to form a stiff, board-like structure. Although the invention has been described with referenee to preferred embodiments, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the preview and the scope of the claims appended hereto.

Claims (40)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An improved fibrous filter material for filtration of fluid media, said media being comprised largely of fibers, which comprises (a) a random-laid filter media formed of a substantial fraction of lignin-containing fibers derived from the disc refining in a substantially dry condition of substantially undelignified wood chips having a lignin content of at least about 10% under steam pressures in the range of about 90 psig to about 120 psig, at temperatures in the range of from about 330°F. to about 350°F., and using energy levels in the range of from about 8 to about 35 HPD/ADT, (b) said disc refining taking place in the absence of substantial liquid medium in said refiner, (c) said lignin-containing fibers being characterized by having most of their original lignin content and by having a smooth wall structure, substantially free of fiber-bonding surface fibrils and being substantially non-self-bonding to adjacent like fibers in the absence of elevated temperatures, (d) said lignin-containing fiber fraction having a freeness of not less than about 725 ml (CSF).

2. Improved filter media according to claim 1, further characterized by (a) said lignin-containing fibers being present in amounts of about 30% or more, in combination with other fibers, (b) said other fibers comprising at least in part fibers from flash dried softwood, flash dried hardwood pulp, alpha pulp, or synthetic fiber, or combinations thereof.

3. Improved filter media according to claim 2, further characterized by (a) said lignin-containing fibers being those capable of passing through circumferentially aligned slots of a rotary screen, in which the slots have a width of about 6 mils, (b) said fibers having a size distribution such that approximately 60% is retained on a 28 mesh screen.

4. The process of making fibrous filter material for the filtration of fluid media, which comprises (a) furnishing a fibrous, substantially undelignified, lignin-containing raw material having a lignin content of at least about 10%, (b) reducing said lignin-containing material to individual pieces of a size appropriate for disc refining, (c) preheating said lignin-containing material pieces by steam at a temperature of from about 330°F. to about 350°F., and a pressure of from about 90 psig to about 120 psig for a period sufficient to enable the material to be heated and the lignin content thereof to be softened, (d) deriving from said raw material lignin-containing fibers having most of their original lignin content by disc refining said preheated material in a substantially dry condition and while maintaining said steam temperature of from about 330°F. to about 350°F. and pressure of from about 90 psig to about 1211 psig and under refiner settings requiring an average energy usage for refining of the lignin-containing material of from about 8 to about 35 HPD/ADT, (e) screening a slurry of said disc refined material to remove oversize fibers and shives, (f) said screened material having a freeness of not less than about 725 ml (CSF), (g) laying the screened, lignin-containing fibers in a random fashion to form a free, porous filter structure with minimum self-bonding between said screened fibers, and (h) imparting to said laid fibers sufficient bonding characteristics to effect at least a minimum degree of bonding between fibers in the region of fiber contact areas.

5. The process of claim 4, further characterized by (a) said lignin-containing material comprising pulp wood logs, (b) said pulp wood logs being initially debarked and then cut into chips having a typical minimum dimension of about 3/8 inch and a typical maximum dimension of about one inch.

6. The proeess of claim 5, further characterized by (a) said pulp wood chips being refined in a double disc, counter-rotating disc refiner, (b) the discs of said refiner being set to provide an outlet peripheral gap which will control the energy usage between about 8 HPD/ADT and about 35 HPD/ADT, during refining of said pulp wood.

7. The process of claim 6, further characterized by (a) mixing the lignin-containing fibers, after refining, with sufficient water to form a screenable slurry, and (b) screening said slurry in a rotatable screen having circumferentially aligned slots for the acceptance and passage of desired fibers.

8. The process of claim 4, further characterized by said lignin-containing material being preheated by steam for a period of approximately three minutes, in direct contact with said steam.

9. The process of claim 8, further characterized by (a) said lignin-containing material comprising chips of debarked pulp wood, (b) said chips having typical minimum dimensions of about 3/8 inch and typical maximum dimensions of about one inch, and (c) said chips being retained in contact with said steam, during the preheating phase, for time sufficient to bring the core of the chip to a temperature of within about 10°F. of the temperature of the steam.

10. An improved fibrous filter material for the filtration of fluid media, comprised largely of fibers, which comprises (a) a substantial fraction of lignin-containg fibers derived from the rotary disc refining in a substantially dry state of substantially undelignified, lignin-containing material having a lignin content of at least about 10%, (b) said lignin-containing fibers having been derived from said disc refining under steam pressures in the range of about 90 psig to about 120 psig and at temperatures in the range of from about 330°F. to about 350°F. and with energy usage in the range of from about 8 to about 35 HPD/ADT, (c) said lignin-containing fibers being combined with other papermaking type fibers and randomly laid to form a web, (d) said web being impregnated with sufficient binder resin to accommodate handling and forming, (e) said lignin-containing fiber fraction having a freeness of not less than about 725 ml (CSF), (f) said lignin containing fiber fraction having a bulk characteristic, when formed into an unpressed sheet, corresponding to a caliper of about 0.040 inch in a sheet having a basis weight of about 65 lbs. (per 3000 sq. ft.)

11. A filter web according to claim 10, further characterized by (a) said lignin-containing fibers containing, in the finished form of said filter web, major amounts of their original lignin content, (b) said lignin-containing fibers being characterized by a smooth wall structure substantially free of fiber-bonding fibrils and being substantially non-self-bonding to adjacent like fibers.

12. A filter web according to claim 11, further characterized by said other paper-making type fibers including any one or more of polyester, cotton linters, or flash dried hardwood.

13. The process of making filter material for the filtration of fluid media, which comprises (a) selecting a source of lignin-containing fibers having an initial lignin content of not less than about 10%, (b) subjecting said lignin-containing fiber source to a preheating treatment for at least about three minutes in a pressurized steam atmosphere at a temperature of from about 330°F. to about 350°F. and at a pressure of from about 90 psig to about 120 psig, (c) thereafter abrasively refining said fiber source in a substantially dry condition and while maintaining a steam atmosphere at a temperature of from about 330°F.
to about 350°F. and pressure of from about 90 psig to about 120 psig, (d) carrying out said refining under energy usage conditions of from about 8 to about 35 HPD/ADT to produce lignin-containing fibers having a smooth lignin-coated outer surface and containing most of their initial lignin content, said lignin-containing fibers having a freeness of at least about 725 ml (CSF), and (e) forming a random-laid mass comprising at least a substantial fraction of said fibers to constitute a filter product having superior dust capacity.

14. The process of claim 13, further characterized by (a) said fiber source comprising debarked pulp wood, and (b) said pulp wood being cut into chips.

15. The process of claim 14, further characterized by said lignin-containing fibers being random-laid in continuous web form and having combined therein fibers from one or more additional fiber sources.

16. The process of claim 15, further characterized by said fibers from additional sources including one or more of flash dried kraft fibers and polyester fibers.

17. An improved, high bulk fibrous filter material for the filtration of fluid media comprising (a) a substantial fraction of lignin-containing fibers derived from the disc refining in substantially dry condition of substantially undelignified lignin-containing material having a lignin content of at least 10%
under steam pressures in the range of about 90 psig to about 120 psig, at temperatures in the range of from about 330°F. to about 350°F. and using energy levels in the range of from about 8 to about 35 HPD/ADT, (b) said lignin-containing fibers being characterized by having most of their original lignin content and by having a smooth wall structure, substantially free of fiber-bonding surface fibrils being substantially non-self-bonding to adjacent like fibers in the absence of elevated temperatures, and having a freeness of at about 725 ml (CSF), and (c) said fibrous material being formed into a random-laid sheet-like structure having a dust capacity of at least about 1460 g/kg.

18. The filter material as defined in claim 17, wherein (a) said lignin-containing fibers are present in amounts of about 30% or more in combination with other fibers, (b) said other fibers comprising at least in part fibers from flash dried softwood, flash dried hardwood pulp, alpha pulp, or synthetic fiber, or combinations thereof.

19. The filter media as defined in claim 18, wherein (a) said lignin-containing fibers are capable of passing through circumferentially aligned slots of a rotary screen, in which the slots have a width of about 6 mils, and (b) said fibers have a size distribution such that approximately 60% is retained on a 28 mesh screen.

20. The filter media as defined in claim 17, wherein the filter media has a void fraction of at least 0.85.

21. The filter media as defined in claim 17, or 20, wherein the filter media has a dust capacity of at least 2190 g/kg.

22. In an automotive-type filter comprising an oil filter, fuel filter or air filter with the filter media thereof being in the form of a cylinder of accordian pleated web material and with said filter media being impregnated with a binder resin, the improvement which comprises (a) said web material being in the form of a random-laid web and comprising a substantial fraction of lignin-containing fibers derived from the disc refining of substantially undelignified lignin-containing material having a lignin content of at least 10%, (b) said material being refined in a substantially dry state under steam pressures in the range of about 90 psig to about 120 psig, at temperatures in the range of from about 330°F. to about 350°F. and using energy levels in the range of from about 8 to about 35 HPD/ADT, (c) said lignin-containing fibers being characterized by having most of their original lignin content and by having a smooth wall structure, substantially free of fiber-bonding surface fibrils and being substantial1y non-self-bonding to adjacent like fibers in the absence of elevated temperatures, and (d) said lignin-containing fibers having a freeness of not less than about 725 (CSF).

23. The automotive-type filter defined in claim 22, wherein said web material has a void fraction of at least 0.80 and has a dust capacity of at least 1460 g/kg.

24. The automotive-type filter defined in claim 23, wherein (a) said web material has void fraction of at least 0.89 and has a dust capacity of at least 2190 g/kg.

25. The automotive-type filter defined in claim 22, wherein (a) said lignin-containing fibers are present in amounts of about 30% or more and in combination with other fibers, (b) said other fibers comprising at least in part fibers from flash dried softwood, flash dried hardwood pulp, alpha pulp, or synthetic fiber, or combinations thereof.

26. The automotive-type filter defined in claim 22, wherein (a) said lignin-containing fibers are capable of passing through circumferentially aligned slots of a rotary screen, in which the slots have a width of about 6 mils, and (b) said fibers have a size distribution such that approximately 60% is retained on a 28 mesh screen.

27. In a process of filtration of a liquid or gaseous medium comprising passing the liquid or gaseous medium to be filtered through filter media, the improvement which comprises (a) passing the liquid or gaseous medium through a random-laid sheet-like mass of high bulk, fibrous filter material which comprises a substantial fraction of lignin-containing fibers derived from the disc refining in a substantially dry state of substantially undelignified lignin-containing material having a lignin content of at least 10%, under steam pressures in the range of about 90 psig to about 120 psig, at temperatures in the range of from about 330°F. to about 350°F. and using energy levels in the range of from about 8 to about 35 HPD/ADT, (b) said lignin containing fibers being characterized by having most of their original lignin content, by having a smooth wall structure substantially free of fiber bonding surface fibrils and being substantially non-self-bonding to adjacent like fibers in the absence of elevated temperature, and (c) said lignin-containing fiber fraction having a pulp freeness of at least about 725 (CSF).

28. The process of filtration defined in claim 27, wherein (a) said lignin-containing fibers are present in amounts of about 30% or more and in combination with other fibers, (b) said other fibers comprising at least in part fibers from flash dried softwood, flash dried hardwood pulp, alpha pulp, or synthetic fiaber, or combinations therof.

29. The process of filtration defined in claim 28, wherein (a) said lignin-containing fibers comprising the filter media are capable of passing through circumferentially aligned slots of a rotary screen, in which the slots have a width of about 6 mils, and (b) said fibers have a size distribution such that approximately 60% is retained on a 28 mesh screen.

30. The process of filtration defined in claim 27, wherein (a) said lignin-containing fibers comprising the filter media are combined with other paper-making type fibers and then randomly laid to form a continuous web, (b) said web then being impregnated with sufficient binder resin to accommodate handling and forming, and (c) said web having a void fraction of at least 0.80 and a dust capacity of at least 1460 g/kg.

31. The process of filtration defined in claim 30, wherein said other paper-making type fibers include any one or more of polyester, cotton or flash dried hardwood.

32. The process of making a high performance, high freeness pulp material, which comprises (a) furnishing a fibrous, substantially undelignified, lignin-containing raw material having a lignin content of at least about 10%, (b) reducing said lignin-containing material to individual pieces of a size appropriate for disc refining, (c) preheating said lignin-containing material pieces for a period sufficient to enable the material to be heated and the lignin content thereof to be softened, (d) deriving from said raw material lignin-containing fibers having most of their original lignin content by disc refining said preheated material while maintaining said steam temperature of from about 300°F to about 350°F
and pressure of from about 50 psig to about 120 psig and under refiner settings requiring an average energy usage for refining of the lignin-containing material of from about 8 to about 35 HPD/ADT, (e) forming a slurry of the disc refined material derived from step (d) and screening said slurry to remove oversize fibers and shives, (f) said screening step including directing the flow of said slurry through circumferentially oriented slots of a cylindrical screen.

33. The process of claim 32, further characterized by (a) said slurry comprising from about 0.5% to about 1% solids.

34. The process of claim 32, further characterized by (a) said cylindrical screen having a slot width of about six mils.

35. The process of claim 32, further characterized by (a) said material being preheated in a steam atmosphere under substantially the same pressure/temperature conditions as are maintained during said refining step, and (b) said preheated material being refined in said pressurized steam atmosphere but otherwise in a substantially dry condition.

36. The process of claim 35, further characterized by (a) said material being preheated and refined under pressures in the range of about 90 psig to about 120 psig and temperatures in the range of from about 330°F to about 350°F, and using refiner energy levels of from about 8 to about 35 HPD/ADT.

37. An improved, high bulk, high freeness pulp material comprising (a) lignin-containing fibers derived from the disc refining of a lignin-containing source material having an initial lignin content of at least 10%, (b) said source material having been disc refined under steam pressures in the range of about 50 psig to about 120 psig, at temperatures in the range of from about 300°F to about 350°F, and using energy levels in the range of from about 8 to about 35 HPD/ADT, (c) said lignin-containing fibers being characterized by having a smooth wall structure, substantially free of fiber-bonding surface fibrils and being substantially non-self-bonding to adjacent like fibers in the absence of elevated temperatures, (d) said lignin-containing fibers having passed through circumferentially aligned slots of a rotary screen.

38. A pulp material according to claim 37, further characterized by (a) the fibers of said pulp having been passed through screen slots of about six mil width.

39. A pulp material according to claim 38, further characterized by (a) said pulp material having a screen analysis such that approximately 60% of the fibers are retained on a 28 mesh screen.

40. A pulp material according to claim 38, further characterized by (a) the screened pulp fibers predominantly having a smooth, fibril-free surface coating of lignin and being relatively straight and rod-like in form.